1. Field of the Invention
The present invention generally relates to methods and apparatuses used in vacuum processing systems used to fabricate integrated circuits, flat panel displays, and other electronic devices. More specifically, the present invention relates to methods and apparatuses for cooling a rotating element in or about a process chamber of a substrate processing system.
2. Background of the Related Art
The processes for fabricating ICs or other structures on a substrate typically involve operating in a vacuum environment in a process chamber. The process chambers include, among others, physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers, rapid thermal processing (RTP) chambers, and etch chambers. Some of these processes involve generating an ionized plasma discharge in a region of the chamber near the substrate to generate ions which strike a target to dislodge target material, which then travel onto the surface of the substrate, thereby depositing a thin film of the target material on the substrate.
Plasma discharges are typically formed in the process chamber by DC or RF voltages, microwaves, planar magnetrons, or a combination of techniques. A planar magnetron system uses a rotating magnetron disposed above a target and either a DC bias between the target and the substrate and/or an RF source coupled into the space between the target and substrate to form the plasma. The magnetron is a magnet assembly that provides magnetic field lines near the sputtering surface of the target. A negative bias voltage between the target and the plasma region accelerates the ions toward the target to dislodge the target material therefrom. The magnetic field from the magnetron confines the free electrons, including secondary electrons displaced from the target material, near the target to maximize the ionizing collisions by the free electrons with the sputtered material. The magnetron typically includes one or more magnets, which rotate around the backside, i.e., non-sputtered surface, of the target to evenly spread the magnetic field around the surface of the target to result in more uniform sputtering of the target material.
FIG. 1 is a schematic side view of a PVD chamber 100. Generally, the PVD chamber 100 comprises a substrate support member 102, a target 104, a cooling cavity 116 and a magnetron 108 disposed therein. A cooling fluid, such as deionized water or antifreeze, flows through the cooling cavity 116 to cool the target 104 and the magnetron 108. The magnetron 108 has a magnet assembly including several magnets 110 mounted thereon. A motor assembly 112 provides rotational motion to the magnetron 108. The plasma is struck in the space between the wafer 114 and the target 104 and ions in the plasma strike the target 104.
The process may heat up the target 104 and the magnetron 108 to about 110.degree. C.-120.degree. C. and about 130.degree. C.-140.degree. C., respectively, in the cooling cavity even with the cooling fluid. If the magnetron 108 and/or the target 104 are heated above a designated process temperature, then the high temperature may alter the performance of the process by changing the sputtering rate or sputtering uniformity on the target and lessening the useful lives of the magnetron 108 and the target 104. Additionally, the excessive heat may cause thermal expansion of the members and cause interference between closely spaced members, such as the target 104 and magnetron 108. The excessive heat may also cause mechanical features of the magnetron 108 to wear out prematurely.
The rotational motion of the magnetron 108 creates a centrifugal force that pulls the cooling fluid away from the rotational center of the magnetron 108 and toward its outer edge. The centrifugal force caused by the rotating magnetron 108 combined with the heat generated at the magnctron's rotational center causes vapor bubbles to form near the rotational center of the magnetron 108, an effect known as cavitation. Additionally, bubbles are formed in the fluid as the fluid is circulated through a heat exchanger (not shown) and then back to the cooling cavity. The bubbles can cause an air pocket to form near the rotational center, reducing circulation. The reduced circulation results in poor cooling near the rotational center of the magnetron. The vapor bubbles also cause an abrasive action on the magnets 110 and cause the magnets 110 to wear.
Others have sought to remedy the problem of poor circulation in the interior portions of the magnetron by creating a low pressure area in the interior portions of the magnetron to induce a cooling fluid flow though the interior portions of the magnetron and promote better circulation, such as in co-pending U.S. application Ser. No. 08/964,949, titled "Magnetron With Cooling System For Process Chamber Of Processing System", filed Nov. 5, 1997. While the induced flow assists in promoting better circulation, the induced flow does not provide a positive forced circulation within the internal portions of the magnetron.
Therefore, a need exists for a mechanism to enhance the flow of cooling fluid through the interior portions of a rotating member, such as a magnetron, in a processing system, such as a PVD chamber.